Separating 2,5-xylenol from a mixture of 2,5-xylenol and 2,4-xylenol

ABSTRACT

A mixture of 2,4-/2,5-xylenol can be alkylated with a suitable alkylating agent over a strongly acidic divinylbenzene-styrene copolymer to afford a greater amount of 4-t-alkyl-2,5-xylenol than 6-t-alkyl-2,4-xylenol provided the alkylation is carried out at a suitably low temperature of up to 60° C.

This invention relates to the selective alkylation of 2,5-xylenol in thepresence of 2,4-xylenol. More specifically, this invention relates to amethod for such alkylation by contacting the 2,4-xylenol/2,5-xylenolmixture with a polymer-bound sulfonic acid catalyst at a temperature ofabout 60° C. or less in the presence of a suitable alkylating agent.

For many applications it is desirable to separate admixtures of2,4-xylenol and 2,5-xylenol into the individual isomers such that eachis available in high purity. These materials cannot be separated byfractional distillation since these isomers boil within 0.1° C. of oneanother. Consequently other methods of achieving this separation must beutilized. The present invention not only provides a method forselectively alkylating 2,5-xylenol in the presence of 2,4-xylenol butalso provides a method for the separation of 2,5-xylenol from2,4-xylenol in a mixture of these isomers using this selectivealkylation followed by a selective dealkylation. The key step in thepresent invention is the selective alkylation of 2,5-xylenol in a2,4-/2,5-xylenol mixture achieved by alkylating this mixture in thepresence of a polymer-bound sulfonic acid catalyst and a suitablealkylating agent at a temperature of up to 60° C. and preferably up to40° C.

The art contains many references relating to phenolic alkylations anddealkylations. The use of polymer-bound sulfonic acid catalysts foralkylation and dealkylation is known. U.S. Pat. No. 2,802,884 describesthe use of a sulfonic acid catalyst on a resin matrix as analkylation/dealkylation catalyst at temperatures greater than or equalto 100° C. Selective alkylation, selective dealkylation, or isomerseparation, however, is not shown.

U.S. Pat. No. 3,584,058 likewise shows such alkylations. Furtheralkylations can be seen from the Journal of Organic Chemistry, Volume22, page 988 (1957).

Processes for the separation and purification of 2,5-xylenol and2,4-xylenol from their admixture are known. Representative but notexhaustive of the prior art is British Pat. No. 582,057 which describesa method for separating 2,4-xylenol and 2,5-xylenol involving thebutylation of a 2,4-/2,5-xylenol mixture and then treating the butylatedmixture with an aqueous alkali solution to yield an aqueous insolubleorganic phase of 6-t-butyl-2,4-xylenol and an aqueous phase of the saltof 4-t-butyl-2,5-xylenol. The aqueous phase is acidified to yield4-t-butyl-2,5-xylenol. Each of the separated butylated xylenols aredebutylated and distilled to afford the purified 2,4-xylenol and2,5-xylenol. British Pat. No. 706,107 teaches that the use of a sulfuricacid catalyst alkylates only 2,4-xylenol with diisobutylene while2,5-xylenol is unchanged. A base is then used to extract unchanged2,5-xylenol. U.S. Pat. No. 2,917,487 shows the separation of2,4-/2,5-xylenol mixtures by selective resinification. German Patent No.1,153,027 teaches separation of 2,4-/2,5-xylenol mixtures by butylationusing isobutylene catalyzed by perchloric acids and the subsequentseparation of the isomeric butylated xylenols by fractionaldistillation. Desired individual isomers are then debutylated.

In copending application Ser. No. 47,190 filed June 8, 1979, I discloseda method for the selective dealkylation of 4-tertiary-alkyl-2,5-xylenolfrom admixture with 6-tertiary-alkyl-2,4-xylenol by contacting themixture of alkylated xylenols with a polymer-bound sulfonic acidcatalyst at temperatures of up to 60° C. and pressures of from about 0.5to 5 atmospheres. The critical step of that invention is the use of asufficiently low temperature to provide selective dealkylation. Thepresent invention, involving critical temperatures for selectivealkylation of a 2,4-/2,5-xylenol admixture allows an even greater use ofmy previous invention since the starting alkylated mixture obtained uponapplication of the present invention is highly favorable for use in thatearlier described process.

The process of the present invention is very similar to that previouslydescribed except for the presence of an alkylating agent. Thealkylation/dealkylation reaction can be carried out under similarconditions. The absence or presence of an alkylating agent determineswhether the xylenols predominantly alkylate (agent present) ordealkylate (agent absent) during a reaction carried out under these sameconditions.

None of the teachings of the prior art indicate a temperature effect tobe critical in such alkylations of 2,4-/2,5-xylenol mixtures. Thepresent invention provides a method for selectively alkylating a2,4-/2,5-xylenol mixture to afford a greater amount of4-t-alkyl-2,5-xylenol than 6-t-alkyl-2,4-xylenol comprising

(a) contacting a 2,4-/2,5-xylenol mixture with an alkylating agent inthe presence of a strongly acidic sulfonated divinylbenzene-styrenecopolymer at a temperature of up to 55° C. and then fractionating theresulting reaction mixture to remove all unreacted xylenols. Removal ofthe unreacted xylenols yields a mixture containing predominantly4-t-alkyl-2,5-xylenol and 6-t-alkyl-2,4-xylenol. This mixture can thenbe selectively dealkylated using the process described in my copendingapplication Ser. No. 47,190 filed June 8, 1979, hereby incorporated byreference in its entirety into the present application. The selectivedealkylation of 4-t-alkyl-2,5-xylenol while an admixture with6-t-alkyl-2,4-xylenol is achieved by contacting a mixture of thesematerials with a strongly acidic polymer-bound sulfonic acid catalyst attemperatures up to or equal to 60° C. and pressures of from about 0.5 toabout 5 atmospheres.

Thus the present invention provides a method for the selectivealkylation of 2,5-xylenol while in the presence of 2,4-xylenol (i.e.yields a greater amount of 4-t-alkyl-2,5-xylenol as compared to6-t-alkyl-2,4-xylenol) by contacting the 2,4-/2,5-xylenol mixture withan alkylating agent which will yield a tertiary-alkyl group in thepresence of a strongly acidic sulfonated divinylbenzene-styrenecopolymer at a temperature of up to 55° C. Application of the processyields upon removal of the unreacted xylenols a large amount of4-t-alkyl-2,5-xylenol which can then be selectively dealkylated in thepresence of a highly acidic sulfonated divinylbenzene-styrene copolymerat a temperature of up to 60° C.

The alkylating agents useful in the instant invention are generallythose which afford a tertiary-alkyl group. Representative examples ofsuch alkylating agents are isobutylene, 2-methyl-1-butene,2-methyl-1-pentene, and 2-methyl-1-heptene. These materials are likewisepreferred. Isobutylene is most preferred and is used throughout in thespecifications to illustrate the instant invention.

The instant invention is carried out at a temperature of 60° C. or lessand preferably at a temperature of 40° C. or less for maximumselectivity. The instant invention is thus highly preferred forprocesses where 2,5-xylenol purification is of primary concern. Theinstant invention yields an alkylated 2,4-/2,5-xylenol mixture which isricher in 4-t-alkyl-2,5-xylenol than 6-t-alkyl-2,4-xylenol. Such amixture is preferred for subsequent selective debutylation steps in2,5-xylenol separation and purification as described in my copendingapplication Ser. No. 47,190 filed June 8, 1979. Direct alkylation of a2,4-/2,5-xylenol mixture using conventional homogenous acidic catalysts,such as sulfuric acid, in contrast produces a greater amount of6-t-alkyl-2,4-xylenol than 4-t-alkyl-2,5-xylenol in the t-alkylatedproduct mixture. The present invention is dependent upon a criticaltemperature limitation.

The instant invention is more concretely described with reference to theexamples below wherein all parts and percentages are by weight unlessotherwise specified. The examples are provided to illustrate the instantinvention and not to limit it.

EXAMPLE 1

A cresylic acid mixture containing 2,4-xylenol and 2,5-xylenol inaddition to other components was used as the cresylic component in thisexample. This mixture consisted of 19.05% 2,3-xylenol, 34.6%2,4-/2,5-xylenols (composition=48.75% 2,5-xylenol and 51.25%2,4-xylenol), 9.88% 2,6-xylenol, 29.31% 2,4,6-trimethylphenol, 3.53%2,3,6-trimethylphenol, 2.89% pentamethylbenzene, and small amounts ofphenol and cresols.

A solution of 748 grams of the above cresylic acid mixture and 254 grams(4.54 moles) of isobutylene was passed through a stainless steelcontinuous tubular reactor having a catalyst bed volume of 66.4 ml. Thereactor was packed with 44 g of dry Amberlyst-15® catalyst (trademark ofand sold by Rohm and Haas Company), a highly acidic sulfonatedstyrene-divinylbenzene copolymer catalyst. During the reaction period,the reactor was maintained at a specific test temperature and a 3 poundsper square inch gauge (psig) backpressure. The feed mixture was pumpedinto the reactor at a rate of 0.94 ml per minute, corresponding to aliquid hourly space velocity (LHSV) of 0.85.

The reaction was begun and the first 93 grams of the product stream wasdiscarded to allow the continuous reaction to come to equilibrium. Theremaining 853 grams of the reaction run were collected and analyzedusing gas chromatography. The following composition was obtained.

Isobutylene: 0.10%

Tertiary Butanol: 0.38%

Isobutylene Oligomers: 9.52%

2,6-Xylenol: 0.76%

2,4-/2,5-Xylenols: 10.13%

2,3-Xylenol: 2.65%

2,4,6-Trimethylphenol: 22.78%

2,3,6-Trimethylphenol: 0.87%

Pentamethylbenzene: 1.35%

6-t-Butyl-2,4-xylenol: 7.77%

4-t-Butyl-2,6-xylenol: 7.20%

6-t-Butyl-2,3-xylenol: 11.46%

4-t-Butyl-2,5-xylenol: 12.04%

1-t-Butoxy-4-t-butyl-2,5-xylene: 0.17%

4-t-Butyl-2,3,6-trimethylphenol: 1.33%

4-6-Di-t-butyl-2,3-xylenol: 8.55%

Unidentified components: 0.3%

In this first experiment, 62.5% of the 2,4-/2,5-xylenol was butylated.

EXAMPLES 2 THROUGH 20

Experiments 2 through 20 were carried out in a similar manner with theresults shown in Table 1.

In this table, the column headed R.T. shows the residence time in thereactor in hours. The column headed M shows the moles of isobutylenedivided by the moles of xylenol in the feed mixture. The column headedConv (IB) is the percent conversion of isobutylene. Conv (24/25) is thepercent conversion of 2,4-/2,5-xylenols, Conv (26) is the percentconversion of 2,6-xylenol, Conv (23) is the percent conversion of2,3-xylenol. The column headed R is the ratio of 4-t-butyl-2,5-xylenolto 6-t-butyl-2,4-xylenol in the product stream.

                                      TABLE 1                                     __________________________________________________________________________    T      P   R.T.    Conv                                                                              Conv                                                                              Conv                                                                              Conv                                           (°C.)                                                                         (psig)                                                                            (Hrs.)                                                                            M   (IB)                                                                              (24/25)                                                                           (26)                                                                              (23)                                                                              R                                          __________________________________________________________________________     1 38  3   1.18                                                                              1.16                                                                              99.6                                                                              62  90  82  1.55                                        2 71  3   1.13                                                                              0.93                                                                              99.7                                                                              46  91  72  0.11                                        3 50  3   1.41                                                                              0.93                                                                              99.5                                                                              53  70  80  1.08                                        4 90  3   1.47                                                                              0.93                                                                              99.6                                                                              37  99  53  0.06                                        5 111 3   2.42                                                                              0.93                                                                              97.7                                                                              23  100 62  0.06                                        6 90  3   0.91                                                                              1.16                                                                              99.4                                                                              43  98  63  0.11                                        7 37  3   0.94                                                                              1.16                                                                              96.5                                                                              57  62  82  1.57                                        8 61  3   1.40                                                                              0.93                                                                              99.9                                                                              44  94  75  0.18                                        9 75  3   1.09                                                                              0.93                                                                              99.8                                                                              42  96  64  0.07                                       10 65  3   1.04                                                                              0.99                                                                              99.8                                                                              54  93  81  0.29                                       11 71  3   1.23                                                                              0.99                                                                              99.8                                                                              48  93  74  0.16                                       12 70  3   2.48                                                                              0.99                                                                              99.8                                                                              48  98  72  0.09                                       13 75  3   1.03                                                                              0.99                                                                              99.8                                                                              47  91  76  0.17                                       14 81  3   1.10                                                                              0.99                                                                              99.7                                                                              46.5                                                                              93  72  0.07                                       15 70  3   1.23                                                                              1.50                                                                              99.5                                                                              70  96  87  0.66                                       16 80  3   1.29                                                                              1.50                                                                              99.7                                                                              57  98  80  0.21                                       17 90  3   1.25                                                                              1.50                                                                              99.6                                                                              50  100 71  0.09                                       18 85  3   1.25                                                                              1.50                                                                              99.6                                                                              57  100 77  0.15                                       19 85  50  1.23                                                                              1.50                                                                              99.8                                                                              51  100 71  0.08                                       20 85  3   1.69                                                                              1.50                                                                              99.7                                                                              57  100 75  0.13                                       __________________________________________________________________________

EXAMPLES 21 THROUGH 30

The cresylic acid mixture whose composition was given in Example 1 wasused. A feed consisting of 950 grams of this material and 440 grams ofisobutylene was pumped into a 300 ml autoclave set up for continuousoperation. The autoclave was equipped with a backpressure regulator,condenser, and liquid sample collector. Samples were collectedperiodically during operation and analyzed by gas chromatrography. Otherruns at varying temperatures were repeated at these differenttemperatures. The results are set forth in Table 2 wherein the columnheadings are the same as those described in Table 1.

                                      TABLE 2                                     __________________________________________________________________________    T      P   R.T.    Conv                                                                              Conv                                                                              Conv                                                                              Conv                                           (°C.)                                                                         (psig)                                                                            (hrs)                                                                             M   (IB)                                                                              (24/25)                                                                           (26)                                                                              (23)                                                                              R                                          __________________________________________________________________________    21 77  3   1.71                                                                              1.33                                                                              93  65  77  84  0.77                                       22 77  2   2.77                                                                              1.34                                                                              96  69  81  86  0.71                                       23 91  2   2.90                                                                              1.34                                                                              97  62  90  86  0.40                                       24 90  2   2.22                                                                              1.56                                                                              95  68  91  85  0.55                                       25 91  2   4.44                                                                              1.56                                                                              98  63  96  85  0.31                                       26 93  3   1.82                                                                              1.73                                                                              93  70  90  87  0.59                                       27 72  3   1.50                                                                              1.73                                                                              92  76  85  86  0.92                                       28 53  3   3.42                                                                              1.73                                                                              96  86  87  89  1.08                                       29 72  3   1.03                                                                              0.93                                                                              96  56  71  77  0.83                                       30 90  3   1.01                                                                              0.93                                                                              98  62  85  80  0.40                                       __________________________________________________________________________

EXAMPLE 31

A sulfuric acid-catalyzed butylation was carried out using a cresylicacid mixture consisting of 89.43% 2,4/2,5-xylenols in a 50/50 ratio,7.40% 2,3-xylenol, 1.25% pentamethylbenzene, and 1.92% of minorunidentified components. A 200 gram sample of the cresylic acid mixtureand 3 grams of concentrated sulfuric acid were placed in a 500 ml3-necked flask equipped with a magnetic stirrer, condenser,thermomometer and gas inlet tube. Isobutylene was bubbled into thestirred solution which was maintained at 35° C. by adjusting the rate ofisobutylene flow and using a combination of external heating and coolingas needed. Small samples were periodically removed for gaschromatographic analysis. The introduction of isobutylene was stoppedafter several hours when the reaction mixture weighed a total of 334grams.

The reaction mixture was poured into a separatory funnel containing 200ml of water. The pH of the aqueous phase was adjusted to 10 by addingdilute caustic. The basic aqueous phase was removed and the reactionmixture was washed with saturated sodium chloride solution. The organicphase was taken up in 200 ml of ether added to break an emulsion. Theresulting ether was washed with several 200 ml portions of water andsaturated sodium chloride solution. This solution was then dried overanhydrous sodium sulfate and the major portion of the ether was removed.The crude product was analyzed by gas chromatography. The gaschromatographic analysis indicated the following composition.

Ether: 3.71%

Isobutylene Oligomers: 12.4%

1-t-Butoxy-4-t-butyl-2,5-xylene: 18.28%

6-t-Butyl-2,4-xylenol: 42.58%

2,4-/2,5-xylenols: 6.58%

4-t-Butyl-2,5-xylenol: 10.93%

Unidentified Components: 5.5%

The relative amounts of butylated and unbutylated 2,4-/2,5-xylenolsobtained by application of the instant invention at 38° C. (Example 1)and from alkylation at 35° C. using sulfuric acid (Example 3) are setforth in Table 3. In Table 3, 2,4-/2,5 indicates 2,4-/2,5-xylenol, 24M6Bindicates 6-t-butyl-2,4-xylenol, 25M4B indicates 4-t-butyl-2,5-xylenol,and Cmpd. A indicates 1-t-butoxy-4-t-butyl-2,5-xylene. The table showsrelative amounts based on 25M4B with a value of 10.0. The values inparenthesis indicate relative amounts based on 100 parts of these foursubstances by weight.

                  TABLE 3                                                         ______________________________________                                                   Polymer-Bound                                                                 Sulfonic Acid Run                                                                            Sulfuric Acid Run                                   Component  Example 1      Example 3                                           ______________________________________                                        24/25       8.4 (33.6)     6.1 (8.4)                                          24M6B       6.5 (25.8)    39.1 (54.3)                                         25M4B      10.0 (40.0)    10.0 (13.9)                                         Cmpd. A     0.1 (0.6)     16.5 (23.3)                                         ______________________________________                                    

It is readily apparent that by using the method of the present inventiona mixture of t-alkylated 2,4-/2,5-xylenols heavily enriched in4-t-alkyl-2,5-xylenol can be obtained; this method consists ofalkylating a 2,4-/2,5-xylenol mixture over a strongly acidic sulfonateddivinylbenzene-styrene copolymer under low temperature conditions. Theresulting t-alkylated mixture after xylenol removal is then useful as afeed for selective dealkylation over the same catalyst at temperaturesof up to 60° C. in an improved method of separating 2,4-/2,5-xylenolmixtures.

While certain embodiments and details have been shown for the purpose ofillustrating this invention, it will be apparent to those skilled inthis art that various changes and modifications may be made hereinwithout departing from the spirit or scope of the invention.

I claim:
 1. A method for separating 2,5-xylenol from2,4-xylenol/2,5-xylenol mixtures comprising(a) preferentially alkylating2,5-xylenol in said mixture in the presence of an alkylating agentselected from the group consisting of isobutylene, 2-methyl-1-propene,2-methyl-1-butene, 2-methyl-1-pentene and 2-methyl-1-heptene and astrongly acidic sulfonated divinylbenzene-styrene copolymer at atemperature of up to 60° C. to yield predominantly4-t-alkyl-2,5-xylenol, (b) fractionating the resulting reaction mixtureto remove all unreacted xylenols, (c) selectively dealkylating4-t-alkyl-2,5-xylenol while in admixture with 6-t-alkyl-2,4-xylenol toyield a mixture containing predominantly 2,5-xylenol and6-t-alkyl-2,4-xylenol by heating the mixture to a temperature of up to60° C. at a pressure of from about 0.5 to about 5 atmospheres in thepresence of a polymer bound sulfonic acid catalyst, then fractionatingthe resulting mixture to separate 2,5-xylenol from the remainingcomponents in the mixture obtained upon selective dealkylation.
 2. Amethod as described in claim 1 wherein isobutylene is the alkylatingagent.
 3. A method as described in claim 2 wherein the the butylationreaction is carried out at a temperature up to 40° C.